This invention relates to a method of bonding a first plate shaped object to a second plate-shaped object by means of an adhesive, wherein the adhesive is applied to one of the two sides of the first object, whereafter said side of the first object and one of the two sides of the second object are pressed together.
The invention also relates to a device for bonding a first plate-shaped object to a second plate-shaped object by means of an adhesive, which device is provided with a first holder having a supporting surface for the first object, a second holder having a supporting surface for the second object, a displacement unit enabling displacement of both holders such that their supporting surfaces face each other, and a pressure unit by means of which the supporting surfaces of both holders can be pressed together.
A method and a device of the type mentioned in the opening paragraph are known from JP-A-07226350. The known method and the known device are used for bonding together two disc-shaped semiconductor substrates by means of an adhesive. The two holders of the known device are arranged in a pressure chamber in which, in operation, the air pressure and air humidity can be controlled. In accordance with the known method, both holders with the semiconductor substrates provided thereon are put in positions, by means of the displacement unit of the known device, in which both semiconductor substrates are arranged so as to be directly adjacent, whereafter both semiconductor substrates are pressed together at a predetermined air pressure and a predetermined air humidity of the pressure chamber by means of the pressure unit of the device. Since both semiconductor substrates are pressed together, the adhesive applied to one of the two semiconductor substrates spreads over a substantial part of the facing sides of the two semiconductor substrates, so that a strong bond between the two semiconductor substrates is achieved.
A disadvantage of the known method and the known device is that the adhesive present between the two semiconductor substrates does not spread completely and homogeneously over the facing sides of the two semiconductor substrates. As a result, using the known method and the known device, a non-homogeneous bond between the two semiconductor substrates is obtained. In addition, the layer of adhesive formed between the two semiconductor substrates has a relatively large thickness, thus limiting the adhesive power present between the two semiconductor substrates.
It is an object of the invention to provide a method and a device of the type mentioned in the opening paragraphs, which makes it possible to obtain a more homogeneous bond between the two plate-shaped objects and a reduced thickness of the adhesive layer between the two plate-shaped objects in comparison with the known method and the known device.
To achieve this, the method in accordance with the invention is characterized in that, at least for a period of time during which both plate-shaped objects are pressed together, they are rotated at equal rotational velocities about an axis of rotation extending substantially perpendicular to said sides of the objects.
To achieve the above-mentioned object, the device in accordance with the invention is characterized in that the device is provided with a rotation unit enabling both holders to be rotated at equal rotational velocities.
Since, in accordance with the inventive method, during the time that the two plate-shaped objects are pressed together, they are rotated about the axis of rotation extending substantially perpendicularly to said sides of the objects, a centrifugal force is exerted on the adhesive present between said sides of both objects. Under the influence of the centrifugal force, said adhesive flows uniformly over said sides of the two objects, so that a relatively thin, homogeneous layer of adhesive is formed between the two objects. In this manner, a relatively strong and homogeneous bond between the two objects is achieved. In addition, since the adhesive spreads uniformly under the influence of the centrifugal force, a compressive force used to press together both objects can be limited. Any excess adhesive is flung away from the outer edges of both objects, so that the excess adhesive does not remain on the bonded objects.
A particular embodiment of a method in accordance with the invention is characterized in that the rotational speed of the plate-shaped objects is changed as a function of the time elapsed in the course of the method (i.e. during a bonding operation).
A particular embodiment of a device in accordance with the invention is characterized in that the rotational speed with which both holders can be rotated by means of the rotation unit adjustable during a bonding operation.
In these particular embodiments of the method and the device in accordance with the invention, the spread of the adhesive. between the two plate-shaped objects and the flinging-away of any excess adhesive from the outer edges of both objects are favorably influenced by changing the rotational speed of both objects in a suitable manner as a function of the time elapsed in the course of the method.
A further embodiment of a method in accordance with the invention is characterized in that, viewed parallel to the axis of rotation, the plate-shaped objects are moved towards each other at an approach speed which is changed as a function of the time elapsed in the course of the method.
A further embodiment of a device in accordance with the invention is characterized in that an approach speed at which both holders can be moved towards each other by means of the displacement unit is adjustable during a bonding operation.
In these further embodiments of the method and the device in accordance with the invention, the spread of the adhesive between the two plate-shaped objects is favorably influenced by changing said approach speed in a suitable manner as a function of the time elapsed in the course of the method.
A still further embodiment of a method in accordance with the invention is characterized in that the plate-shaped objects are pressed together with a compressive force which is changed as a function of the time elapsed in the course of the method.
A still further embodiment of a device in accordance with the invention is characterized in that a compressive force with which the supporting surfaces of the two holders can be pressed together by means of the pressure unit is adjustable during a bonding operation.
In these still further embodiments of the method and the device in accordance with the invention, the spread of the adhesive between the two plate-shaped objects is favorably influenced by changing said compressive force in a suitable manner as a function of the time elapsed in the course of the method.
A particular embodiment of a method in accordance with the invention is characterized in that the plate-shaped objects are rotated, during a first phase in which the second object already is in contact with the adhesive applied to the first object, at a predetermined rotational speed and are moved towards each other at a predetermined approach speed, while the objects are rotated, during a subsequent second phase, at a further predetermined rotational speed and pressed together with a predetermined compressive force.
A particular embodiment of a device in accordance with the invention is characterized in that, in operation, during a first phase, the two holders are rotatable by means of the rotation unit at a predetermined rotational speed, and can be moved towards each other by means of the displacement unit at a predetermined approach speed, while during a subsequent second phase, both holders can be rotated by means of the rotation unit at a further predetermined rotational speed and can be pressed together with a predetermined compressive force by means of the pressure unit.
In these particular embodiments of the method and the device in accordance with the invention, adhesive is applied in excess to the first plate-shaped object. During said first phase, the plate-shaped objects are rotated at a relatively low rotational speed and moved towards each other at a relatively low approach speed. In this manner, it is achieved that the adhesive spreads very uniformly over the facing sides of both objects and penetrates as much as possible into any irregularities present on said sides. A relatively large part of the adhesive applied to the first object is flung away from the outer edges of the objects. During said second phase, the objects are rotated at a relatively high rotational speed and pressed together with a relatively large compressive force. In this second phase, it is achieved that the adhesive present between the objects spreads further to form a relatively thin homogeneous layer of adhesive, so that a strong bond between the two objects is achieved. By virtue of the relatively high rotational speed, the necessary compressive force is limited, while the outer edges of the objects to be bonded together remain substantially free of adhesive.
A further embodiment of a method in accordance with the invention is characterized in that, in accordance with the method, a disc-shaped semiconductor substrate and a disc-shaped support for the semiconductor substrate are bonded together. This further embodiment of the method in accordance with the invention is employed in the manufacture of so-called SOA-semiconductor devices (Silicon-On-Anything). In this manufacturing process, the method in accordance with the invention is used to bond a disc-shaped semiconductor substrate to an insulating support of, for example, glass or synthetic resin. Such a disc-shaped semiconductor substrate comprises a large number of identical semiconductor devices which, after the semiconductor substrate has been bonded to the support, are separated from each other. Since the adhesion of each individual SOA-semiconductor device thus obtained should be of a good quality, the bond between the original semiconductor substrate and the support should be as homogeneous as possible. Thus, the advantages of the method in accordance with the invention become particularly manifest if the method is used in the above-described manner to manufacture said SOA-semiconductor devices.
A further embodiment of a device in accordance with the invention is characterized in that the device is provided with a receiving chamber for adhesive, which is arranged around at least one of the holders. Any excess adhesive which, during rotation of two plate-shaped objects which are to be bonded together, is flung away from the outer edges of the objects is caught in the receiving chamber arranged around the relevant holder provided that the rotational speed of both holders is sufficient, so that the flung-away adhesive does not cause contamination of other parts of the device.
Yet another embodiment of a device in accordance with the invention is characterized in that at least one of the two holders is provided with a ring of blades around its supporting surface. The ring of blades provided around the supporting surface of the relevant holder causes, during rotation of the holders with the plate-shaped objects provided thereon, an increase of the air flow along the outer edges of the objects, so that the discharge of excess adhesive from the outer edges of the objects is improved.
A particular embodiment of a device in accordance with the invention is characterized in that, viewed in a direction of rotation of the holders, both holders are coupled to each other. As both holders are coupled to each other, viewed in the direction of rotation, during rotation of the holders with the plate-shaped objects provided thereon, an angular displacement of the objects relative to each other in the direction of rotation is precluded, so that the adhesion between the objects is not disturbed by such an angular displacement.
A further embodiment of a device in accordance with the invention is characterized in that both holders are accommodated in a rotor housing which can be rotated by means of the rotation unit, both holders being coupled to the rotor housing, viewed in the direction of rotation. The use of said rotor housing enables both holders to be coupled to each other in the direction of rotation in a simple and practical manner.
These and other objects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.